1. Field of the Invention
The invention relates to a method for performing an internal exhaust gas recirculation into the combustion chamber of an internal combustion engine, especially a diesel engine, with an intake valve stroke of at least one intake valve being performed during an exhaust cycle.
2. The Prior Art
In order to take the more stringent exhaust emission legislations into account and to realise the best possible fuel mileages, it is increasingly necessary in diesel engines to admix a certain quantity of exhaust gas to the fresh air taken in by the engine. The NOx emissions of the engine are thus reduced to the quantity demanded by the legislator while maintaining a favourable utilisation of the fuel.
In the case of supercharged utility vehicle diesel engines, the mean pressure in the exhaust manifold (depending on the engine size and the speed band) is lower than on the intake side over a wide speed and load margin, which would obstruct exhaust gas recirculation via a simple connection line between the exhaust manifold and the intake side of the engine.
The internal exhaust gas recirculation offers the possibility, independent of the pressure conditions in the intake and exhaust section, to recirculate gas back to the cylinder.
An internal combustion engine with internal exhaust gas recirculation into the combustion chamber is known from DE 34 37 330 A1, in which the intake valve is opened for a short time during the exhaust cycle, with the opening occurring not earlier than 30° crank angle after the lower dead centre prior to gas exchange and the maximum stroke being between 15% and 30% of the maximum intake valve stroke. Shortly before the upper dead centre of the gas exchange there is still a minimum opening of the intake valve which remains until the start of the intake stroke, whereas the exhaust valve closes before the upper dead centre of the gas exchange. In this way, however, it is only possible to realise optimal exhaust gas recirculation quantities in the partial-load range, while the quantity of recirculated exhaust gas decreases towards full load and no exhaust gas is recirculated any more at full load. The minimal opening of the intake valve during the entire exhaust stroke leads to the additional disadvantage that the flow in the intake section is disturbed.
AT 3207 U1 describes a method for performing an internal exhaust gas recirculation into the combustion chamber of an internal combustion engine. In order to enable internal exhaust gas recirculation in the full-load range, an intake valve pre-stroke of at least one intake valve is performed during the exhaust stroke, with the start of the intake valve pre-stroke occurring before 180° crank angle after the upper dead centre of the ignition. If the intake start of the intake valve pre-stroke is defined at such an early time, an internal exhaust gas recirculation occurs at low speed. This is highly undesirable, however, because there will be increased development of smoke due to lack of air.
An air-compressing internal combustion engine is known from DE 1 242 044 C in which in one embodiment the intake valve is opened briefly after the beginning of the exhaust stroke in order to form the preconditions for the formation of a wear-reducing protective layer on the intake valve seats. The wear-reducing protective layer is formed by still lubricating combustion residues. There is no further information in the specification on the opening of the intake valve during the exhaust stroke.
It is the object of the present invention to avoid the aforementioned disadvantages and to improve the emissions in a diesel combustion engine both in the high and low speed ranges.